Abstract
We differentiate between the success of a classical biological control programme and its impact; the former addressing the completed implementation of the steps of a biological control programme, and the anticipated reduction of the target pest, and the latter addressing the societal and environmental benefits of control of the target pest. We provide ten case studies in which CABI has played a role to illustrate aspects of success and impact for biological control programmes against insects pests and weeds: cassava mealybug (Phenacoccus manihoti), mango mealybug (Rastrococcus invadens), pink hibiscus mealybug (Maconellicoccus hirsutus), orthezia bug (Insignorthezia insignis), brown peach aphid (Pterochloroides persicae), banana skipper (Erionota torus), black sage (Varronia curassavica), rubber vine (Cryptostegia grandiflora), leafy spurge (Euphorbia esula) and water hyacinth (Eichhornia crassipes). In light of these we discuss the assessment of success and impact of biological control programmes, why these aspects are often not adequately addressed, how they might be retroactively addressed and the implications for donor-funding of biological control programmes for developing countries.